Multistage flash evaporator-condenser arrangement



May 6, 1969 L EvrrE 3,442,765

MULTISTAGE FLASH EVAPORATOR-CONDENSER ARRANGEMENT A TTRNE YJ,

' G. LEVITE May 6, 1969 MULTISTAGE FLASH EVAPORATOR-CONDENSERARRANGEMENT Sheet Filed OCC. 5, 1966 GIDEON av United States Patent U.S.Cl. 202-173 7 Claims ABSTRACT OF THE DISCLOSURE A multi-stage flashevaporator, wherein the condenser means for a given stage is locatedbelow the portion of the evaporator wherein flashing of distilland tovapor occurs, whereby a decrease in pumping requirements for the entireevaporator is realized.

'Ihis invention relates to the construction of ash evaporators.Moreparticularly, this invention relates to a novel arrangement ofinternal elements in ash evaporators.

It is well-known to distill saline fwater or waters having otherdissolved impurities by means of ash evaportion to obtain puredistillates. Thus, in the past, it has been the usual practice toevaporate sea water, scrub entraned droplets from the resulting vapor,pass the vapor around a condenser medium, and collect the resultingcondensate beneath the condenser medium. IIn the past, numerous types ofevaporation apparatus have been proposed wherein the unevaporatedportion of the saline or turbid water is mixed with incoming water andrecycled through the apparatus.

A shortcoming of prior art apparatus has been high capital costs,particularly due to high shipping costs, or alternatively, high costs ofon site construction. Thus, the interior portions of conventionalevaporators, particularly the condenser section, which includes a largebundle of tubular members, is heavy and relatively fragile. Accordingly,such element requires particular care in shipping. Moreover, since inconventional practice the condenser section is located at the top of theapparatus, relatively heavy underpinnings must be built into theevaporator to support the condenser section. Such heavy constructionincreases the cost of material and labor in manufacture, and results inhigher shipping costs. Moreover, to successfully handle hot recycleliquid, it has been necessary to place recycle pumps in deep wellsbeneath the apparatus, thereby further increasing the cost ofconstruction.

Another shortcoming of conventional evaporators using recycle techniqueshas been the need for high pumping energy. The pump used to recycle theunashed liquid must, in the usual case, supply sucient pressure toovercome line pressure losses and to prevent premature flashing of therecycle liquid in the lines.

Accordingly, it is one object of the present invention to provide aliash evaporator wherein the requisite pumping energy is reduced.

It is another object of the present invention to provide an evaporatorconstruction having decreased construction and installation cost.

It is still another object of the present invention to provide a ilashevaporator capable of easier shipping than evaporators heretofore known.

Other objects will appear hereinafter.

The present invention resides in a ash evaporator construction wherein acondenser section is located within an evaporator shell, below anevaporator section. Such a construction results in inherently lowerpumping energy requirements, lower construction costs and a lighterweight ice structure, with attendant savings in material, labor andshipping costs.

lFor the purpose of illustrating the invention there are shown in thedrawings forms which are presently preferred; it being understood,however, that this invention is not limited to the precise arrangementsand instrumentalities shown.

FlGURE l is a longitudinal cross-sectional view of a conventional ashevaporator of the multi-stage type.

BIGURE 2 is a transverse cross-sectional view of the evaporator ofFIGURE 1 taken along line 2 2 in FIG- URE 1.

FIGURE 3 is a transverse cross-sectional view of one form of anevaporator in accordance with the present invention.

FIGURE 4 is a transverse cross-sectional view of another form of anevaporator in accordance with the present invention.

FIGURE 5 is a transverse cross-sectional view showing stillanother formof a flash evaporator in accordance with the. present invention.

EIGURE 6 is a partial cross-sectional view comprising a llsh evaporatorembodying the principles of the present invention with a typical priorart evaporator.

Referring to the drawings in detail, wherein like numerals indicate likeelements, there is shown in FsIGURE l a, conventional llash evaporatordesignated generally by the reference numeral .10. The flash evaporator10 includes heat rejection stage or stages i12. The ash evaporator 10also includes a series of heat recovery stages 14, the number of stagesbeing variable.

The heat rejection stage 12 includes a condenser section 18, whichcontains condenser tubes 20. Also, the heat rejection stage y12 includesan evaporator section 22 and a Acondensate collection pan 24.

IReferring now to the extreme left of FIGURE 1, distilland, usually rawsea rwater, is conducted to the apparatus through a conduit 26. Theconduit 26 is in fluid communication with one end of the condenser tubes20 of the condenser section 118i. The opposite ends of the condensertubes 20 are in fluid communication with the conduit 28. A branchconduit 30 joins the conduit 28 and serves as a bleed. A recycle conduit32 interconnects a lower portion of the evaporator section 22 with theconduit 28 for a purpose to be made clear shortly. A bleed conduit 36emanates from the recycle conduit 32.

A product conduit 38 is in communication with one of its ends with thecondensate collection pan 24. A product pump 40 serves to remove theproduct from the product conduit 38.

Referring now to the heat recovery stages 14, it is seen that suchstages are contained within an outer shell or pressure vessel 42. Thevessel 42 contains spaced vertically oriented transverse Walls orpartitions, which divide the vessel into a series of stages. Each stagecomprises a condenser section 46 and an evaporator section 50i.Condenser tubes 48 run through the vessel 42. Thus, the condenser tubes48 run through the respective condenser section of each heat recoverystage. A condensate pan S2 extends the length of the vessel 42, andlikewise, passes through each of the stages.

In operation, raw distilland enters the apparatus through the conduit26, passes through the condenser tubes 20 and conduit 28, and thecondenser tubes 48. Also, the uid from the recycle conduit 32 joins theincoming distilland in conduit 28. Thus, the combined distilland andrecycle liquid serve as a condenser medium for each stage of the device.From the condenser tubes 48 the distillandrecycle mix passes to a brineheater 16, a conduit 54 and a pressure reducing valve 56 The valve 56prevents premature llashing of the combined distilland and the recycleliquid downstream of the recycle pump. The liquid then re-enters thevessel 42. It should be understood that the initial heat recovery stageis maintained at a pressure below the saturation pressure correspondingto the temperature of the incoming liquid, and accordingly, as theliquid enters the stage, a portion is flashed to vapor. Such vapor risesupwardly into the condenser section 46, wherein it comes into contactwith the relatively cool condenser tubes 48, and condenses. Resultingcondensate falls to the condensate pan 52. Thus, referring to FIGURE 2,it is seen that in rising to the condenser section 46, the vapor passesthrough tine mesh screens 58, which serve to remove any entrained liquidparticles. The screens 58, it should be understood, are one example ofacceptable vapor scrubbing means. Those skilled in the art willrecognize that alternative constructions may be used, or in someinstances, the scrubbing means may be omitted.

The remaining mixture flows through a pressure reducing and sealing baie60 in the wall or partition 44 into the next stage, wherein it re-ashes.In a similar manner, the remaining mix passes from stage to stage of theheat recovery stages 14, and then through the conduit 62 to theevaporator section of the heat rejection stage 12.

Similarly, the condensate in the condensate pan 52 ows through pressurereducing and sealing bafes 64 to successively lower stages of the heatrecovery stages, and then through the conduit 66 to the condensate pan24 of the heat rejection stage.

A common shortcoming of prior art evaporators of the type shown inFIGURE l stems from the need to locate the recycle pump 34 low enough toavoid ashing of liquid in the conduit 32 upstream of the pump. Thepresent invention, as embodied in FIGURES 3 to 6 represents a simple andeconomical solution to the above problem.

Referring now to FIGURE 3, there is seen a crosssection of a flashevaporator in accordance with the present invention. The flashevaporator 10 includes an outer shell or pressure vessel 68 in which thetrough 70 is disposed. It should be understood that the vessel 68 is`divided by walls or partitions 72 into stages, in a manner not unlikethe recovery stages 14 of the evaporator 10. Condenser tubes 74, theconstruction and functions of which are similar to the aforementionedcondenser tubes 48, extend through the vessel 68 below the trough 70.The mixture flows in the trough 70 in vapor contact with the interior ofthe vessel 68 in each successive stage. A portion of the mixture owingin the trough 70, upon entering a given stage, ashes to vapor. Suchvapor moves downwardly into contact with the condenser tubes 74. Thecondenser tubes 74, it will be understood, contain a liquid condensingmedium. Thus, vapor in contact with the condenser tubes 74 is condensed,and eventually drops to the bottom portion 78 of the vessel 68. Suchbottom portion defines a means whereby liquid distillate may becollected. Fine mesh screens 80 or other scrubbing means may be providedin connection with the trough 70 for removing entrained droplets ofunilashed liquid from the vapors rising fromthe trough.

A conduit 82 is connected to the trough 70 and the recycle pump 84. Thepump 84 discharges into a conduit 86, which in turn is in uidcommunication with the condenser tubes 74. Thus, the trough 70 is influid communication with the condenser tubes 74 through the conduit 82,pump 84 and the conduit 86.

An important aspect of the present invention is illustrated by the lineA-C-B in FIGURE 3. Thus, the distance A-B denotes the vertical distancefrom the surface of liquid in the trough 70 to the inlet of the recyclepump 84. Those skilled in the art will appreciate that the difference instatic tluid pressure at the two extremes of the line A-B may beexpressed as the mass density of the uid times the vertical distanceA-B. Such difference in pressure is of great importance in the operationof the device, since liquid removed from the trough 70 is at itssaturation pressure and hence, a real danger of dashing in the conduit82 and pump 84 exists. Flashing in the conduit 82 would interfere withthe ow of recycle liquid and flashing in the pump itself results incavitation, and consequently, the possibility of severe mechanicaldamage, As was indicated above, prior art apparatus such as theevaporator 10 overcame the problem by placing the recycle pump 84 in adeep well below the evaporator, and accepted the disadvantage ofincreased capital costs due to the deep well. With the present novelarrangement of elements, the vertical distance from A to the bottom ofthe vessel 68, which is wholly above ground, represents an inherentsaving in well depth. Furthermore, the distance A-C, that is thedifference between the level of the liquid in the trough 70 and thecondenser tubes, represents a pressure head for preventing prematureashing downstream of the pump 84. Such head is almost whollyrecoverable, and this, a saving in pumping energy is realized. Bycomparison, referring to FIGURE 6, with conventional structure thedistance from the surface of the distilland in evaporator section 22 tothe inlet of the recycle pump 34, equivalent to the distance A-B, wouldbe almost entirely outside the evaporator and almost wholly located in adeep well. The valve 56, shown in FIGURE l, prevents ashing downstreamof the pump, but the head due to such valve is not recoverable.

FIGURE 4 shows yet another evaporator construction embodying theprinciples of the present invention. In the embodiment shown in FIGURE4, the evaporator 10" includes troughs 88 and 90, each disposed abovethe condenser tubes 92. Fine mesh screens 94 and 96 are provided toscrub entrained liquid from vapors rising from the troughs 88 and 90 inthe previously described. The embodiment of FIGURE 4 represents aconvenient way of increasing the capacity of an evaporator constructedin accordance with the principles of the present invention.

Yet another evaporator in accordance with the present invention is setforth in FIGURE 5. The evaporator 98 set forth in FIGURE 5 comprises ashell or pressure vessel 100, containing a trough 102. Also disposed inthe vessel 100 are condenser tubes 104 and a condensate receiving tray106. It should be apparent that the bottom portion 108 of the pressurevessel 100 serves as a further means for conducting distilland throughthe several stages of the evaporator 98. Thus, in operation, thedistilland is simultaneously conducted through the pressure vessel 100by the trough 102 and bottom portion 108, thereby creating two sourcesof vapor. Scrubbers` and 112, which may take the form of fine meshscreens are associated with the trough 102 and with the bottom portion108 for removing entrained liquid droplets from the vapor. Those skilledin the art will appreciate that the embodiment shown in FIGURE 5represents somewhat of a hybrid development, and contains certainfeatures of the prior art devices, while partaking of the advantagesinherent in the construction shown in FIG- URE 3.

In each of the above-described embodiments of the present invention,significantly lower capital costs than are currently typical for plantsof the equivalent capacity are realizable. Such reductions in capitalcosts are due to several factors. Among these are the savings realizedby eliminating the cost of construction of a deep well for the recyclepump. Also, a saving is realized through decreased pumping energyrequirements. Moreover, the heaviest parts of each of these embodiments,namely the condenser tubes, are located relatively low in the structure.Accordingly, heavy structural parts, normally used to support thecondenser tubes and located in the upper portion of the evaporator, arein some cases eliminated, and in all cases located at a lower portion ofthe structure. Such structures may therefore be made lighter than thoseheretofore known, and due to their lower centers of gravity, are stableduring shipment. Accordingly, shipping costs are substantially reduced.

In view of the foregoing, it is evident that the novel flash evaporatorconstructions herein disclosed constitute a clear advance in the art.

The present invention may be embodied in other speciic forms withoutdeparting from the spirit or essential attributes thereof and,accordingly, reference should be made to the appended claims, ratherthan the foregoing specitication as indicating the scope of theinvention.

I claim:

1. A flash evaporator comprising a generally horizontally disposedpressure vessel, a plurality of generally vertical partitions withinsaid pressure vessel dividing said vessel into a plurality ofhorizontally spaced stages of successively lower pressure, means forconducting liquid distilland generally horizontally through said vesselfrom stage to stage in vapor contact with the interior of said vessel ineach successive stage so that a portion of said distilland is made toHash to vapor in each stage, condenser means comprising tubes forconducting a liquid condensing medium from stage to stage out of directcontact with the vapor, said condenser means being disposed below saidmeans for conducting distilland, means disposed below said condensermeans for collecting liquid distillate, said tubes of said condensermeans being in fluid communication with said means for conductingdistilland so that distilland may be initially pre-heated as the liquidcondensing medium and then introduced into said means for conductingdistilland, a recycle loop in uid communication with said means forconducting distilland and said tubes of said condenser means, and saidrecycle loop including a pump, said pump :being disposed below thesurface of the distilland in said means for conducting distilland by avertical distance sufficient to provide a static pressure head at theinlet of said pump to prevent flashing of distilland in the recycleloop.

2. A ash evaporator in accordance with claim 1 wherein said means forconducting distilland through said vessel comprises a trough.

3. A ash evaporator in accordance with claim 1 wherein said means forconducting distilland through said vessel comprises a generallyhorizontally extending trough, and scrubbing means associated with saidtrough for removing entrained liquid particles from the vapor.

, means and a bottom portion of said pressure vessel definingk a furthermeans for conducting distilland from stage to stage.

7. A tiash evaporator in accordance with claim 6 and means associatedwith said bottom portion of said pres- Ysure vessel and said means forconducting distilland for removing entrained liquid particles from thevapor.

References Cited UNITED STATES PATENTS 3,342,697 9/ 1967 Hammond 203-112,289,956 7/1942 Gaus et al 202-188 X 3,330,739 7/1967 Roe et al. 203-113,096,256 7/ 1963 Worther et al 202-173 3,119,752 1/ 1964 Checkovich202-173 X A 3,203,875 8/ 1965 Sturtevant 203-11 X 3,228,859 1/1966Fankel et al. 202-173 3,245,883 4/1966 Loebel 203-11 X 3,304,242 2/1967Lockman 202-173 3,320,137 5/1967 Jebens et al 203-11 X 3,334,024 8/1967Zahavi 202-173 OTHER REFERENCES The Institution of Mechanical Engineers:Flash Evaporators for the Distillation of Sea Water by A. Frankel.(1960) pp. 5, 6, 9, 11 and 15.

NORMAN YUDKOFF, Primary Examiner. F. E. DRUMMOND, Assistant Examiner.

U.S. C1.X.R.

